Specific design criteria are proposed to mitigate radiated emissions from a resonant enclosure excited by a heat sink acting as a microstrip patch antenna source. In this particular application, the EMI mechanism is assumed to be due to coupling from the dominant TMz010 mode to one or more resonant modes associated with the enclosure dimensions. The enclosure is then presumed to radiate, at the enclosure resonance frequencies, through one or more apertures, slots, or seams. The EMI-reduction strategy consists of shifting the resonant frequency of the dominant-patch antenna mode by dielectrically loading the patch antenna with thermal-gasket material baying a specified electric permittivity. Specific formulas and graphs will be presented showing how to select the electric permittivity of the thermal-gasket material in order to obtain a given frequency shift. A comparison of experimental measurements with the predictions of the design criteria indicates that frequency shifts of up to approximately three times the bandwidth of the patch resonance can be predicted with reasonable accuracy. In at least two different commercial products that we are aware of, changing the electrically insulating heat sink gasket materials has solved specific radiated EMI problems.


Electrical and Computer Engineering

Research Center/Lab(s)

Electromagnetic Compatibility (EMC) Laboratory

Keywords and Phrases

1 to 3.5 GHz; EMI Considerations; EMI-Reduction Strategy; UHF Antennas; Apertures; Coupling; Design Criteria; Dielectric-Loaded Antennas; Dominant TM010Z Mode; Dominant-Patch Antenna Mode; Electric Permittivity; Electrically Insulating Heat Sink Gasket Materials; Electromagnetic Coupling; Enclosure Dimensions; Enclosure Resonance Frequencies; Frequency Shift; Heat Sinks; Heat-Sink-Thermal-Gasket Materials; Microstrip Antennas; Microstrip Patch Antenna; Patch Antenna; Patch Resonance; Permittivity; Radiated Emissions; Radiofrequency Interference; Resonant Enclosure; Resonant Frequency; Resonant Modes; Seams; Electromagnetic Interference; Microstrip Antenna; Resonance

International Standard Serial Number (ISSN)

0018-9375; 1558-187X

Document Type

Article - Journal

Document Version

Final Version

File Type





© 2001 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Aug 2001